The prior art discloses light modules and methods for generating wavelength-converted light by means of wavelength conversion elements, such as phosphors, for example, in which excitation light, for example monochromatic light from a laser diode, is radiated onto the phosphor and the latter emits light having a converted, usually higher, wavelength. In the case of phosphors, as is known the problem occurs that they exhibit a decrease in the conversion efficiency with an increase in the pump power and pump power density of the excitation light. An increase in the pump power leads to an increase in the average temperature and, by way of the temperature dependence of the conversion efficiency, to a saturation of the output power (thermal quenching). A further cause that leads to a saturation of an output power in the event of an increase in the pump power density is intensity quenching, that is to say that a reduced population density of the lower pump level of the phosphor occurs on account of the long lifetime of the involved activator states of the phosphor. There is also a further problem in that these effects, such as thermal quenching and intensity quenching, are manifested to different extents in the case of different phosphors. Especially red phosphors exhibit a very great reduction of the conversion efficiency in the event of an increase in the pump power.
FIG. 1 shows, in a schematic illustration of a diagram, the dependence of the radiation power Φe, that is to say the converted output power, on the pump power PP for a yellow phosphor 10, a green phosphor 11 and a red phosphor 12 for an identical excited phosphor area. As can be discerned, in this case the conversion efficiency of the red phosphor 12 is significantly lower than that of the yellow phosphor 10 and of the green phosphor 11. Furthermore, it can also be discerned that the conversion efficiency of the red phosphor 12 decreases to a significantly greater extent than that of the yellow phosphor 10 and of the green phosphor 11 as the pump power PP increases.
In the case of light modules, such as projectors, for example, in which different phosphors are used for generating e.g. green, yellow and red light, the limitation of the pump power in the red channel leads to a lower red luminous flux, which limits the total luminous flux of the projectors or adversely influences the white point. The prior art currently furthermore involves the use of red phosphors with as little thermal quenching as possible. However, these red phosphors then have a short dominant wavelength in the orange-red range that leads to a reduction of the size of the addressable color space. However, alternatively available LEDs for the red channel having a longer dominant wavelength likewise limit the total luminous flux in hybrid projectors on account of their low luminance.